Dynamic Load Balancing in an EVPN-VXLAN Network

Benefits of Dynamic Load Balancing in an EVPN-VXLAN Network

• More efficient use of aggregated Ethernet links that share a common ESI.

• Better bandwidth utilization throughout an EVPN-VXLAN network.

How Dynamic Load Balancing Works

Figure 1 shows a sample EVPN-VXLAN network in which we support dynamic load balancing. This network includes the following elements:

• Multihomed Hosts 1 and 2. Each of the hosts is connected to two leaf devices through an aggregated Ethernet LAG that is assigned a common ESI.

• Multihomed Leafs 1 through 4. Each of the leaf devices is connected to Spines 1 and 2.

Figure 1: EVPN-VXLAN Network with Dynamic Load Balancing

In this EVPN-VXLAN network, the leaf devices perform dynamic load balancing. To understand how dynamic load balancing works, here’s what happens when Host 1 sends a packet to Host 2. In addition to the following dynamic load balancing explanation, Figure 2 provides a graphical summary of the path options and the choices made.

• Host 1 must choose one of the aggregated Ethernet interfaces through which to forward the packet. In this case, Host 1 chooses the interface to Leaf 1.

• Upon receipt of the packet, Leaf 1 identifies Host 2’s destination MAC address 00:00:5E:00:53:AA as a member of remote ESI 00:15:25:35:45:55:65:75:85:95. This ESI is assigned to aggregated Ethernet interface ae0, to which Leafs 3 and 4 are connected.

• Leaf 1 can choose either Leaf 3 or 4 as the intermediate Layer 2 EVPN-VXLAN next hop to which to forward the packet. Using packet parameters established by the dynamic load balancing feature, Leaf 1 dynamically chooses Leaf 3.

• Leaf 1 can choose either Spine 1 or 2 as the next hop to reach Leaf 3. Using Layer 3 routing tables and routes programmed into the switch hardware, Leaf 1 chooses Spine 1.

Figure 2: Summary of Path Options and Choices

How Traffic Is Balanced

Juniper Networks switches use a hash of the following packet parameters to dynamically select the next-hop VTEP:

• Packets with an IP header:

  • IP header fields:

    • Source IP address

    • Destination IP address

    • Protocol

  • VLAN ID

  • Layer 4 (TCP and UDP) source and destination ports

• Packets with an MPLS/IP header:

  • Up to three top labels

  • IP header fields:

    • Source IP address

    • Destination IP address

  • Layer 4 (TCP and UDP) source and destination ports

• Packets with a Layer 2 header only:

  • Source MAC address

  • Destination MAC address

  • VLAN ID

The hashing takes place before a packet undergoes VXLAN encapsulation.

To refine the hashing input used by dynamic load balancing, you can include the enhanced-hash-key hash-parameters ecmp configuration statements at the [edit forwarding-options] hierarchy level.

How to Verify That Dynamic Load Balancing Is Enabled

You can verify that dynamic load balancing is enabled by entering the following command:

user@switch> show ethernet-switching global-information
Global Configuration:

MAC aging interval    : 300         
	...
LE  VLAN aging time   : 1200        
RE state              : Master      
VXLAN Overlay load bal: Enabled     
VXLAN ECMP            : Enabled     

In the output that appears, check the VXLAN Overlay load bal field to make sure that it is set to Enabled.